1. Field of the Invention
The present invention relates to an apparatus and method thereof for inspecting optical members, mostly optical members made of plastic, and more particularly relates to an apparatus and method for inspecting optical members using image processing technology.
2. Description of the Related Art
Recently, optical members made of plastic have been widely used in photographing lens systems or finders of cameras, due to their lightweight and low-cost qualities.
However, with such optical members there is a possibility that dust, e.g., in the form of carbonated plastic, remains in the mold after injection molding and thus might enter inside a lens being molded. Additionally, since plastic is softer than glass, there is a higher possibility of a flawed lens being produced, and therefore inspection for defects before assemble has an increased importance.
Defect inspection is undertaken in order to judge whether an optical member has sufficient performance to be used, namely whether it is non-defective and useable, or is defective and can not be used.
In the prior art, defect inspection is usually either in the form of visual inspection by the naked eye, in which a skilled worker illuminates the optical member, such as a lens or prism, by an intense light, or in the form of image processing of an inputted image obtained by picking-up an image of the optical member.
If dust has entered a lens, factors such as the size of the dust, the depth of entry, or the distance from the optical axis, need to be determined. On the other hand, if there is a flaw, factors such as the size of the flaw, the surface on which the flaw is, or the distance of the flaw from the optical axis, need to be determined.
The criteria used for judging whether an optical member is defective or non-defective, is different depending on whether dust has entered the member or whether there is a flaw, for example, even in the case that the dust and the flaw have the same size, one may be allowable, e.g., the dust, while the other type of defect, e.g., the flaw, is not. Therefore, an inspector should judge whether the lens is defective or non-defective, not only from the extent of the defect, but also from the identification of the type of defect, i.e., whether it is dust or a flaw.
In visual inspections by the naked eye, a judgement as to whether a lens is defective or non-defective is subjective according to each individual inspector, and thus judgement criteria may change according to the physical condition of the same inspector, e.g., in the weakening of the eyes, to say nothing of the judgement criteria of a different inspector, thus making it difficult to maintain unitary judgements.
The present invention is made considering the problems of the prior art as described above. An object of the present invention to provide an optical member inspection apparatus and method of inspection thereof capable of judging the defectiveness of an optical member according to objective criteria.
Another object of the present invention is to provide an optical member inspection apparatus capable of obtaining the most appropriate luminance in accordance with the shape of an object to be inspected.
Yet another object of the present invention is to provide an optical member inspection apparatus capable of obtaining the most appropriate luminance in accordance with the color of a defect.
Still another object of the present invention is to provide an optical member inspection apparatus capable of obtaining the most appropriate luminance for detecting defects according to the type of an object to be inspected.
Another object of the present invention is to provide an apparatus capable of being used for an optical member, as a subject for inspection, that has a function of a wedge prism which deflects light in one direction.
Another object of the present invention is to provide an optical member inspection apparatus and method of inspection thereof provided with a magnification adjustment function capable of setting magnification according to objective criteria.
Still another object of the present invention is to provide an optical member inspection apparatus, in regard to an inspection apparatus by using image processing, capable of promptly detecting a defect of an object to be inspected.
Another object of the present invention is to provide an optical member inspection apparatus capable of detecting a mold mark separated from other defects using image processing.
Yet another object of the present invention is to provide a method of mark separation capable of separating a mark accurately through simple processing, from an input image obtained by picking-up an image of an optical member, and also provides an optical member inspection apparatus using the same method.
Still another object of the present invention is to provide a method of efficient inspection in the case of a sequential inspection of optical members in regard to a plural number of items to be inspected, and also provide an optical member inspection apparatus using the method.
Another object of the present invention is to provide an optical member inspection apparatus and method of inspection thereof, for which it is not necessary to execute complicated image processing for the removal of noise etc., while the subject inspection range is wider than the designed effective aperture.
Yet another object of the present invention is to provide an optical member inspection apparatus capable of expediting the duration of inspection in the case of a sequential inspection of a plural number of objects to be inspected.
Still another object of the present invention is to provide a method of controlling of lighting luminance, according to a histogram of a picked-up image, and also provides an optical member inspection apparatus using the same method.
To achieve the objects mentioned above, according to an aspect of the present invention, an optical member inspection apparatus is provided having an inspection optical system having a light source, and a diffusing means for diffusing the light emitted from the light source. The diffusing means has a central portion and a peripheral portion. The diffusion transmittance of the peripheral portion is higher than the diffusion transmittance of the central portion. The inspection optical system also has an image pick-up means to pick-up an image of the optical member to be inspected, and is positioned so as to receive that light emitted from the light source and transmitted through the diffusing means and the optical member. A judging means is also provided, for judging whether or not the optical member has a defect, in accordance with image signals output from the image pick-up means.
Preferably, the diffusing means consists of a plane plate member, having central and peripheral portions, extending substantially perpendicular to an optical axis of the image pick-up means. However, first and second diffusing plates, together determining the central and peripheral portions, could also be used as the diffusing means. The shapes of the central and peripheral portions, are preferably determined according to the shape of the optical member to be inspected. In addition, it is also preferred that the central and peripheral portions are each variable in shape, and that the optical member inspection apparatus includes means for setting each shape.
The diffusing means preferably consists of a liquid crystal panel having a plurality of segments, each segment having a diffusion transmittance that can be varied according to a voltage applied thereto. The setting means sets the shape of the peripheral and central portions by controlling the voltage applied to each segment.
Preferably, a wavelength selecting means is provided for selecting a wavelength of that light incident on the optical member. The wavelength selecting means can vary the spectral transmittance of the central and peripheral portions.
In addition, a means for moving at least the diffusing means in a direction along the optical axis of the image pick-up means, is preferably provided.
The diffusing means preferably consists of first and second diffusing plates, each placed approximately perpendicular to the optical axis of the image pick-up means, and each having a uniform diffusion transmittance. The second diffusing plate is positioned at a center of the first diffusing plate so as to form the central portion. With such an arrangement, the moving means can preferably move at least the second diffusing plate in the optical axis direction. However, the moving means could be selected to move both the light source and the diffusing means, as a whole, in the optical axis direction.
It is preferred that the optical member inspection apparatus also has a means for moving the light source relative to the diffusing means, in a direction along the optical axis of the image pick-up means, so that light can be projected towards the diffusing means at a predetermined emission angle.
It is also preferred that means are provided for moving at least the diffusing means in a direction perpendicular to the optical axis of the image pick-up means, and that a lighting unit, consisting of the light source and the diffusing means, are moved, by the moving means, in the direction perpendicular to the optical axis of the image pick-up means.
Using the optical member inspection apparatus of the present invention, there is provided a method for inspecting an optical member, consisting of firstly, positioning the diffusing means such that light transmitted through the optical member and picked-up by the image pick-up means, substantially corresponds to light transmitted through the central portion of the diffusing means. Secondly, an image of the optical member is input from the image pick-up means, and thirdly, according to the input image, it is judged whether or not the optical member is defective.
Preferably, the image pick-up means can be adjusted by adjusting magnification.
The optical member inspection apparatus preferably further consists of a means for displaying an image of the optical member picked-up by the image pick-up means. A reference value storing means is also preferably provided, in which a value of a reference outline of the optical member and a recommended magnification of the image pick-up means are registered for each type of the optical member. A means for calculating a reference frame using the reference outline value and the recommended magnification read from the reference value storing means, in accordance with a type of the optical member, is also preferably provided. In addition, a means is preferably provided for calculating a magnification of the image pick-up means, in order to make an outline of an image of the optical member, picked-up by the image pick-up means, coincide with the reference frame. A means for adjusting the magnification of the image pick-up means, according to the magnification calculated by the magnification calculating means, is also preferably provided.
The magnification adjusting means preferably consists of first and second storing means, for respectively storing a size of the outline of the picked-up image of the optical member, and a size of the reference frame. By comparing the sizes stored in the first and second storing means, the magnification adjusting means adjusts the magnification of the image pick-up means.
In another aspect of the present invention an optical member inspection apparatus is provided, in which light emitted from a lighting means and transmitted through an optical member to be inspected is picked-up by an image pick-up means for inspecting a defect of the optical member. The lighting means emits low and high luminance light towards the optical member. The low luminance light is emitted parallel to an optical axis of the image pick-up means, while the high luminance light is emitted inclined relative to the optical axis of the image pick-up means.
In a further aspect of the present invention, a method is provided for inspecting an optical member, in which light emitted from a light source is diffused by a diffusing means before being made incident on the optical member. The light emitted from the optical member is picked-up by an image pick-up means. The diffusing means includes central and peripheral portions. The diffusion transmittance of the peripheral portion is higher than the diffusion transmittance of the central portion. The method consists of firstly, inputting an image, including an image of the optical member, from the image pick-up means. Secondly, the image of the optical member is separated from the input image. Thirdly, the image of the optical member is binarized, using a primary threshold value lower than an average luminance of the image of the optical member. Fourthly, the image of the optical member is binarized, using a secondary threshold value higher than the average luminance of the optical member image, and fifthly, it is judged whether or not the optical member is defective by taking first and second binarized signals as defects of different types.
According to a further aspect of the present invention an optical member inspection apparatus is provided consisting of a light source, and a diffusing means for diffusing light emitted from the light source. The diffusing means consists of central and peripheral portions. The diffusion transmittance of the peripheral portion is higher than the diffusion transmittance of the central portion. An image pick-up means, positioned to receive light emitted from the light source and transmitted through the diffusing means and the optical member, is also provided to pick-up an image of an optical member to be inspected. The image pick-up means is adjustable in magnification. A reference value storing means is provided, in which a value of a reference outline of the optical member and a recommended magnification of the image pick-up means are registered for each type of the optical member. A means for calculating a reference frame using the reference outline value and the recommended magnification, read from the reference value storing means, in accordance with a type of the optical member, is also provided. In addition, a means for displaying the reference frame, superimposed on an image of the optical member picked-up by the image pick-up means, is provided.
In a further aspect of the present invention, a method is provided for inspecting an optical member, in which light emitted from a light source is diffused by a diffusing means, consisting of central and peripheral portions, before being made incident on the optical member. Light emitted from the optical member is picked-up by an image pick-up means. The diffusion transmittance of the peripheral portion is higher than the peripheral portion of the central portion. The method consists of firstly, inputting an image, including an image of the optical member, from the image pick-up means. Secondly, separating the optical member image from the input image. Thirdly, calculating a reference frame using a value of a reference outline of the optical member and a recommended magnification of the image pick-up means. The calculated reference frame and the calculated recommended magnification are prestored according to the type of the optical member. Fourthly, a magnification of the image pick-up means is adjusted, so that an outline of an image of the optical member, picked-up by the image pick-up means, may coincide with the reference frame, and fifthly, it is judged whether or not the optical member is defective, according to an image of the optical member picked-up by the image pick-up means at the adjusted magnification.
According to a further aspect of the present invention, a method is provided for inspecting an optical member, in which light emitted from a light source is diffused by a diffusing means, before being made incident on the optical member. The light emitted from the optical member is picked-up by an image pick-up means. The diffusing means includes central and peripheral portions, with the diffusion transmittance of the peripheral portion being higher than the diffusion transmittance of the central portion. The method consists of the processes of firstly, inputting an image of the optical member from the image pick-up means. Secondly, the input image is binarized and a preliminary separating operation is executed, in which the image of the optical member is roughly separated from the input image according to a luminance distribution of the binarized input image. Thirdly, it is judged whether or not the preliminary separating operation has been successfully executed. If it is judged that the preliminary separating operation has been success the a main separating operation is executed, in which an image to be inspected is separated from the roughly separated image of the optical member, and fifthly, the separated image to be inspected is binarized to judge whether or not the optical member is defective.
Preferably, in the above method, the preliminary separating operation is executed such that a rectangular section, including the image of the optical member, is separated from the input image, according to a luminance distribution in an X-axis direction and a Y-axis direction. The X-axis direction and the Y-axis direction being perpendicular with each other.
It is preferred that the above-mentioned fifth process consists of binarizing the separated image to be inspected that is separated in the preliminary separating operation, using a primary threshold value. The primary threshold value being lower than an average luminance of the separated image to be inspected. Secondly, the separated image to be inspected that is separated in the preliminary separating operation is binarized using a secondary threshold value. The secondary threshold value being higher than the average luminance of the separated image to be inspected, and thirdly, it is judged whether or not the optical member is defective by taking first and second binarized signals, obtained respectively through the two binarizing processes, as defects of different types.
According to still another aspect of the present invention, an optical member inspection apparatus is provided including means for picking-up an image of an optical member to be inspected, to output the image of the optical member. The output image of the optical member is binarized by provided means, to detect a suspected mold defect. A first plurality of counters, each counting a number of appearances of the suspected mold defect at a common position on a plurality of optical members molded by a common mold, are also provided. When the number of appearances reaches a first predetermined number, means are provided for deciding that the suspected mold defect appearing at the common position is a real mold defect.
Preferably, a second plurality of counters, are also provided, each counting the number of non-appearances of the suspected mold defect at the common position during a period the suspected mold defect fails to appear, before the number of appearances has reached the first predetermined number. The number of the first plurality of counters is identical to the number of second plurality of counters. First and second reset means are also provided, for respectively resetting one counter in the first plurality of counters when the number of non-appearances in a corresponding counter in the second plurality of counters reaches a second predetermined number, and for resetting one counter in the second plurality of counters when the suspected mold defect reappears at the common position before the number of non-appearances of the one counter in the second plurality of counters has reached the second predetermined number.
In yet another aspect of the present invention an optical member inspection apparatus is provided consisting of means for picking-up an image of an optical member to be inspected, to output the image of the optical member. Means for provided for binarizing the output image of the optical member to detect a suspected mold defect. A first plurality of counters and a second plurality of counter are provided, for each counting a number of appearances of the suspected mold defect at a common position on a plurality of optical members molded by a common mold, and for each counting a number of non-appearances of the suspected mold defect at the common position during a period the suspected mold defect fails to appear, before the number of appearances has reached a first predetermined number, respectively. The number of the first plurality of counters being identical to the number of second plurality of counters. First and second reset means are provided for respectively resetting one counter in the first plurality of counters when the number of non-appearances of a corresponding counter in the second plurality of counters reaches a second predetermined number, and for resetting one counter in the second plurality of counters when the suspected mold defect reappears at the common position, before the number of non-appearances of the one counter in the second plurality of counters has reached the second predetermined number. Additionally, means are provided for deciding that the suspected mold defect at the common position is a real mold defect, when the number of appearances reaches the first predetermined number.
In another aspect of the present invention, a method is provided for separating an image of a mark, formed on an optical member to be inspected, from an image of the optical member input from an image pick-up means picking-up an image of the optical member. The method consists of firstly, binarizing the input image of the optical member to draw (extract) a figure corresponding to the mark or a defect of the optical member from the binarized input image. Secondly, a binarized image of a reference mark having no defect is expanded. Thirdly, a primary image is generated, including a figure corresponding to the mark and a figure corresponding to the defect, the defect being located in a vicinity of the figure corresponding to the mark, by executing an AND operation of the binarized input image and the expanded binarized reference mark per pixel. Fourthly, the image of the mark is generated by removing all figures of defects not connected to the figure corresponding to the mark from the primary image, in accordance with information regarding the reference mark, and fifthly generating an image excluding the image of the mark, by extracting the image of the mark generated from the binarized input image.
Preferably, the figures included in the primary image are numbered in order of size from a largest to a smallest. The number of numbered figures being identical to the number of reference marks. A non-numbered figure or figures amongst the figures included in the primary image, being eliminated to thereby generate the image of the mark.
According to another aspect of the present invention, there is provided an optical member inspection apparatus for judging whether or not an optical member to be inspected is defective. The optical member having a mark formed thereon. The optical member inspection apparatus including a means for picking-up an image of the optical member, to output an image of the optical member. Means are provided for binarizing the image of the optical member, and for drawing (extracting) a figure corresponding to the mark or a defect of the optical member from the binarized input image. In addition means are provided for expanding a binarized image of a reference mark having no defect. First, second and third generating means are provided for respectively generating a primary image including the figure corresponding to the mark and a figure corresponding to the defect, the defect being located in a vicinity of the figure corresponding to the mark, by executing an AND operation of the binarized input image and the expanded binarized reference mark per pixel, and for generating the image of the mark by removing all figures of defects not connected to the figure corresponding to the mark from the primary image, in accordance with information regarding the reference mark, and for generating an image excluding the image of the mark, by extracting the image of the mark generated by the second generating means from the binarized input image. Additionally, means are provided for judging whether or not the optical member is defective, in accordance with at least one of the image of the mark generated by the second generating means and the image excluding the image of the mark that is generated by the third generating means.
Preferably, the third generating means numbers figures included in the primary image in order of size from a largest to a smallest. The number of numbered figures being identical to the number of reference marks. In addition, the third generating means eliminates a non-numbered figure, or figures, amongst the figures included in the primary image, to thereby generate the image of the mark.
In yet a further aspect of the present invention, there is provided a method of inspecting a plurality of optical members, each optical member being inspected by a plurality of types of inspection, to detect a defect. In this method, the type of inspection having the higher frequency of detection of the defect, the earlier the type of inspection is executed. The frequency of detection being statistically obtained.
Preferably, in the case where one optical member, amongst the plurality of optical members to be inspected, is judged to be defective in one type of inspection, the remaining types of inspection are not executed on the defective optical member.
According to yet another aspect of the present invention, there is provided an optical member inspection apparatus for inspecting a plurality of optical members, each optical member being inspected by a plurality of types of inspection, to detect a defect. In this optical member inspection apparatus, the higher a frequency of detection of the defect in one type of inspection, amongst the plurality of types of inspection, is, the earlier that inspection is executed. The frequency of detection being statistically obtained through an inspecting operation.
In yet another aspect of the present invention, an optical member inspection apparatus is provided having a plurality of image inputting means provided respectively for a plurality of types of inspection. Means are provided for consecutively supplying an optical member to be inspected to respective image input positions of the plurality of image inputting means, and means are provided for judging that the optical member is defective, when a defect of more than a predetermined value is detected on the optical member in at least one type of inspection amongst the plurality of types of inspection. A supply order controlling means for controlling the supplying means in accordance with a frequency of existence of the defect for each of the plurality of types of inspection, is provided. The frequency of existence being statistically obtained through an inspecting operation, so as to firstly supply the optical member to one of the image input positions corresponding to a type of inspection in which a frequency of detection of the defect is higher than any other type of inspection amongst the plurality of types of inspection.
According to another aspect of the present invention, an optical member inspection apparatus is provided consisting of means for picking-up an image of an optical member to be inspected, to output the image of the optical member. Means for setting a plurality of areas to be inspected in the image of the optical member, is also provided. One of the plurality of areas is an outermost area including a boundary line defining a designed effective aperture of the optical member. In addition, means are provided for setting a criterion for judgement for each of the plurality of areas, the criteria being different from one another. A criterion set for the outermost area is alleviative, compared with the other criteria. Means are also provided for judging whether or not each of the plurality of areas is defective, in accordance with a corresponding criterion from the criteria set by the criterion setting means.
In a further aspect of the present invention, there is provided a method of inspecting an optical member to judge whether or not the optical member is defective. A plurality of areas to be inspected are set in an image of the optical member, picked-up by an image pick-up means. A criterion for judgement is set differently for each of the plurality of areas. The method consisting of firstly, setting an outermost area, including a boundary line defining a designed effective aperture of the optical member, as one of the plurality of areas. Secondly, the optical member for the outermost area is inspected with a predetermined criterion, from the set criteria. The predetermined criterion being alleviative, compared with the other criteria.
According to another aspect of the present invention, there is provided an optical member inspection apparatus consisting of placing means for consecutively placing each of a plurality of optical members to be inspected, firstly, at a first position, where each image of an optical member is picked-up, and subsequently at a second position, where each optical member is stamped with a predetermined mark. Means for picking-up an image of each optical member at the first position, to output an image, are also provided. In addition, means are provided for judging whether or not each optical member is defective, according to the image of the optical member output from the image pick-up means, and means for stamping the predetermined mark on each optical member at the second position, depending on a judgement of the judging means regarding the optical member, are also provided. The placing means conveys one optical member to be inspected, which has not yet been inspected, to the first position, while conveying another optical member to be inspected, which has been already inspected at the first position, to the second position.
Preferably, the stamping means stamps the mark only when the optical member is judged to be defective by the judging means.
In another aspect of the present invention, a method is provided including a first process of inspecting an optical member to judge whether or not the optical member is defective, and a second process of stamping a mark on the optical member depending upon a result of the inspection. The first and second processes are performed at different positions at the same time.
In yet another aspect of the present invention, a method of inspection and marking is provided, consisting of inspection and marking process. In the inspection process, it is inspected whether or not an optical member to be inspected is at an inspection position. In the marking process a mark is stamped on the optical member at a marking position, different from the inspection position, according to a result of inspection of the inspection process. An optical member to be inspected, which has not yet been inspected, is conveyed to the inspection position while another optical member to be inspected, which has been already inspected at the first position, is being conveyed to the second position.
According to a further aspect of the present invention, there is provided a method of controlling a luminance of light emitted from a light source used in an inspection apparatus for inspecting an optical member. The light emitted from the light source is transmitted to means for picking-up an image of the optical member through the optical member, an image output from the image pick-up means being image-processed to obtain an image of the optical member. The method consists of firstly, forming a histogram showing a luminance distribution of the image of the optical member by a number of pixels. Secondly, a threshold value is obtained according to a discriminant analysis method, based on the histogram, and thirdly, the luminance of light emitted from the light source is controlled, in accordance with the threshold value.
In another aspect of the present invention, there is provided a method of controlling a luminance of light illuminating an object to be inspected. The method consists of firstly, obtaining a threshold value according to a discriminant analysis method, based on a histogram of an image of the object, and secondly of controlling the luminance of light, in accordance with the threshold value.
According to a further aspect of the present invention, an optical member inspection apparatus is provided having means for lighting an optical member to be inspected. Means are also provided for picking-up an image of the optical member, lighted by the lighting means, to output an image of the optical member. Means for image-processing the image of the optical member so as to inspect the optical member, are also provided. In addition, there is provided means for forming a histogram which shows a luminance distribution of the image of the optical member by a number of pixels, and means for obtaining a threshold value according to a discriminant analysis method, based on the histogram, and for controlling a luminance of light emitted from the lighting means in accordance with the threshold value.
According to still another aspect of the present invention, an optical member inspection apparatus is provided, which picks-up an image of an object to be inspected, lighted by lighting means, and judges whether or not the object is defective according to the image of the object. The light emitted from the lighting means has a luminance distribution which clearly differentiates between a luminance of an area to be inspected, including an image of the object, and a luminance of a background area, excluding the object image, in the image. The luminance of light emitted from the lighting means being controlled in accordance with a threshold value obtained according to a discriminant analysis method.
The present disclosure relates to subject matter contained in Japanese patent applications No.7-164825 (filed on Jun. 7, 1995), No.7-164826 (filed on Jun. 7, 1995), No.7-164827 (filed on Jun. 7, 1995), No.7-172911 (filed on Jun. 15, 1995), No.7-175518 (filed on Jun. 19, 1995), No.7-175519 (filed on Jun. 19, 1995), No.7-184795 (filed on Jun. 28, 1995), No.7-189844 (filed on Jul. 3, 1995), No.7-189853 (filed on Jul. 3, 1995), No.7-208398 (filed on Jul. 24, 1995), No.7-208399 (filed on Jul. 24, 1995), No.7-208400 (filed on Jul. 24, 1995), No.7-221120 (filed on Aug. 7, 1995) and No. 8-101834 (filed on Apr. 1, 1996) which are expressly incorporated herein by reference in their entireties.